1. Field of the Invention
The invention relates to a process and a device for measuring the value of the average gas torque by combustion of an internal combustion heat engine, and, more specifically, to processes and devices for correcting the value of this average gas torque by combustion as a function of certain operating parameters such as the rate of recirculation of the exhaust gases, the rate of residual burnt gases and excess oxidant (air) .
2. Description of the Related Art
In an internal combustion heat engine, the torque produced is the resultant of many parameters and reflects the adequacy of their settings. It constitutes the output of a complex dynamic system. Its measurement is relatively simple and usual on a test-bed, but the cost of this measurement is relatively high. Further, the usual measuring beds deliver only the average values on several combustion cycles of the torque of the engine in stabilized operation. Such measurements of average values over a large number of combustion are insufficient in many respects, for example, for optimizing certain settings of the engine or for diagnosing certain operating defects. Of these defects, detection and statistical evaluation of combustion misfiring are necessitated by new international regulations.
To achieve the above objectives, the quantitative analysis of the average gas torque by combustion produced by the combustion of the gas mixture in the various cylinders of the heat engines is necessary. Such an analysis so far has been made only in the laboratory or on very high-power engines, and it generally relies on increases of pressure in the combustion chambers. This technique exhibits the major drawback of being able to be used only on engines designed (or specially modified) to make possible an installation of pressure sensors. In addition, it obviously is not immediately applicable to engines routinely mounted on a vehicle and, further, it remains so, as long as the reliability, the cost, the life and the convenience of use of the pressure sensors are not in accordance with the economic requirements of the automobile industry.
In a PCT international patent application, filed by Motorola Inc. and published on Jun. 20, 1990 under No. WO 90/07051, an electronic control system of the operation of an internal combustion heat engine is described. This system is based on the concept that the instantaneous value of the advancement period of the teeth of a measuring ring gear, integral with the inertial flywheel of the engine, and in front of a stationary sensor, corresponds to the measurement of the instantaneous power output successively produced in each of the cylinders of the engine. The signal thus produced by the sensor is accordingly processed. This processing consists in: (1) measuring the instantaneous period d.sub.i of advancement for the teeth of the ring gear in front of the sensor, (2) respectively multiplying periods d.sub.i of the teeth relating to each of the cylinders by given weighing factors P.sub.i belonging to a sequence corresponding to a particular operating criterion of the engine such as pinging or power output (the procedure for determining these factors is not described), (3) adding results d.sub.i.P.sub.i obtained for each cylinder, (4) comparing this sum to a particular value taken as reference, (5) deducing, if necessary, from the result of this comparison the presence of pinging in a cylinder or a power imbalance of a cylinder relative to the others and (6) consequently modifying the supply to the cylinder of an air-fuel mixture.
The object of the system thus described is to eliminate all pinging in the cylinders of the engine and/or to balance the instantaneous power outputs provided by each of them. As a result, the absolute value of the various intermediate magnitudes obtained is neither desired nor found.
In the copending patent application filed by Applicants on the same date as the present application and titled: "PROCESS AND DEVICE FOR MEASURING THE TORQUE OF AN INTERNAL COMBUSTION HEAT ENGINE," which is hereby incorporated by reference, a device is described for producing a value Cg, representative of the average gas torque produced by each combustion of the gas mixture in the cylinder or cylinders of an internal combustion heat engine. This device comprises measuring reference points placed on a ring gear integral with the inertial flywheel of the engine or integral with the crankshaft, means for defining an indexing reference per flywheel revolution or per camshaft revolution for the reference points, an advancement sensor of the reference points mounted stationary in the vicinity of the ring gear, means for producing a primary value d.sub.i representative of the period of advancement of each of the reference points in front of the sensor, means for processing this primary value d.sub.i and thus producing two secondary values, respectively representative of average angular velocity .OMEGA..sub.m of the reference points during a period of the combustion in the engine and, for the same period of the combustion, representative of the Ecos.phi. projection on the phase reference line, groups of reference points respectively relating to the combustion in the various cylinders of the engine, of alternating component E of instantaneous angular velocity .OMEGA..sub.i of the reference points at the frequency of the combustion in the engine, and means for combining these two secondary values, according to an equation: EQU Cg=-a..OMEGA..sub.m Ecos.phi.+b..OMEGA..sup.2.sub.m
and thus producing the desired value, terms a and b being constants determined experimentally.
In the particular case of a four-cycle, four-cylinder gasoline engine which operates according to the four-stroke cycle, each of the four periods of the cycle (intake, compression, combustion-expansion, exhaust) occurs during a particular half-revolution of the inertial flywheel integral with the crankshaft of the engine. The kinetic energy acquired by the system concerned (crankshaft, flywheel and alternating weights) is the result of various positive and negative instantaneous torques exerted on it during each of the different periods of the operation cycle of the engine.
Torque Cg, calculated for each half-revolution in the special case above, is produced during the compression and combustion expansion phases of the gas mixtures respectively trapped in two contiguous combustion cylinders. Since the engine is equipped with four cylinders in the case being considered, the two other cylinders are in intake and exhaust phases and it is possible to demonstrate as a first approximation that they do not affect the value of Cg because of the cos.phi. projection. Since the compression phases are less subject to variations, i.e., to dispersions, than the combustion-expansion phases, it is possible to conclude that the value of Cg calculated on a half-revolution is that relative to the cylinder which was firing. It is also possible to conclude that torque Cg is an estimation of the average gas torque in the two phases, compression and combustion-expansion, of the same cylinder therefore trapping the same gas mixture.
Regardless of the engine, Cg is, on the one hand, normally positive and, on the other hand, balanced by the sum of resistant average torques coming from variations of the rotary inertias of the engine, of various internal frictions in the engine, of intake vacuums and of exhaust excess pressures of the other cylinders and, of course, of the load, i.e., the vehicle.
The theorem of the kinetic energy teaches that the elementary variation of the kinetic energy of a system equals the elementary work of the torques to which they are subjected. By applying this theorem to the system concerned, namely the crankshaft, the inertial flywheel and the alternating weights involved, and by assuming that the crankshaft-flywheel unit is rigid, using a harmonic analysis of the result obtained, the load placed downstream from the inertial flywheel being considered as totally uncoupled for the frequency being considered, it is demonstrated that the alternating component Ca of the gas torque at the frequency of the combustion in the engine is linked to average angular velocity .OMEGA.m of the inertial flywheel and to the projection, on a phase reference line, of alternating component E of instantaneous angular velocity .OMEGA..sub.i of this flywheel, at the frequency of the combustion of the engine, by the following linear equation: EQU Ca=-a.sub.1..OMEGA..sub.m.Ecos.phi.b.sub.1..OMEGA..sup.2.sub.m
in which a.sub.1 and b.sub.1 are two constant terms, the first proportional to the rotary inertia of the engine and the second, a function of the moment of inertia of the alternating masses and, in some cases of measurement, irregularities of position of the reference points of the measuring ring gear.
Further, an experimental study on the test-bed of several internal combustion heat engines has shown that the Cg/Ca ratio of average value Cg of the gas torque and of alternating component Ca of the same gas torque varies little for the various speeds and for the various operating loads of the engine concerned, especially since richness (r) of the gas mixture is constant or greater than or equal to one.
Consequently, the experimentation and the calculation for a rigid crankshaft-flywheel system have made it possible to produce the equation EQU Cg=-a..OMEGA..sub.m.Ecos.phi.+b..OMEGA..sup.2.sub.m
which is at the origin of the process and the measuring device for the low speeds of the engine as described and claimed in the above-mentioned patent application.
In the case of high operating speeds of the engine, this basic equation must, however, undergo a correction. Actually, at high speed, the torsional elasticity of the engine linkages, particularly that comprised by he crankshaft and the inertial flywheel of the engine, exhibit a frequency transfer function which modifies vector E which is representative of the basic alternating component of the instantaneous angular velocity of the flywheel at frequency fi of the combustion in the engine. Since the links have insignificant damping, the transfer function can be written Z=1+(fi/fr).sup.2, term fi being the combustion frequency proportional to rotation frequency fv of the flywheel (fi=fv.2k/t) with k the number of cylinders and t the number of periods of the operating cycle of the engine and fr the frequency of mechanical resonance in torsion of the crankshaft/flywheel connection. In practice, this frequency fr is equal to four to six times the maximum rotation frequency in Hertz of the engine, so that term z=(fi/fr).sup.2 relative to combustion frequency fi will often be low and so that a simple correction factor (1-z) can be applied to constant "a" of the basic equation referred to above, so that calculated value Cg is corrected for the "crankshaft/flywheel torsion" effect.
In the above-mentioned copending patent application, the influence on the calculation of Cg of the recirculation of exhaust gases (RGE), of the presence of residual burnt gases (GBR) and of excess oxidant (air) in the cylinders have not been taken into account.